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To re gear or not, that is the question


New Member
Jul 20, 2022
Country Flag
Hi guys, thius is my first post on this forum.
I am fitting a set of 33x12.5x15 on my vehicle from the standard 31s and would like to get the vehicle back to as close to standard gear ratios as possible afterwards.
From my data plate it would seem that my car has 4.1 diff ratios. I will need 4.36 to be exactly where it is currently.
My question is whether I will be able to fit the 4.3 crownwheel and pinion onto the existing 80 fiff center without changing out the whole diff center. The two diff centers are not the same and to convert from one to the other is just not economically viable.
In short is it possible to remove the crownwheel and pinion only from a 100 series and bolt it to the 80 diff center carrier?
Thanks for any advice you can give me.
Regearing for 33s is absolutely not needed. It would be a huge and unnecessary expense and effort for no practical gain. If you just want to correct the speedo there are modules available to do this.
35x12.5x15 on my 24 valve 4.2 diesel 80 and i think i'd regret regearing because it runs great as is .
+1 - re-gearing and it's associated costs makes sense for 35" and up. (diesels notwithstanding)
While I noticed a difference when I went to 33's, it's not so bad that a re-gear was absolutely necessary.
But I can tell that 35's will definitely require a re-gear...prob in the 4.88 range in case I want to try 37's (which is the top end for 4.88 generally).
Thanks for all the responses guys, I am in the process of acquiring a set of 33s to do a test. My biggest concern is fuel economy with the current fuel prices. I have heard figures of an increase in the region of 12% in fuel which is unacceptable to me for such a small mod. I should have some numbers in a couple of weeks and will report here.
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Nope - you'll not notice any significant difference in fuel use (remember the speedo and mileage will under-read slightly with the bigger tyres) - certainly nothing approaching the cost of a re-gear (you might recoup the cost in 20 or 30 years, I guess). Circumference difference in 31 to 33 is only +6.5%.
Depends on your tyres though , grippy mud tyres have a lot more rolling resistance than road tyres . But size wise once its rolling a larger diameter tyre actually carries you a little further with each rotation so you might actually save fuel on a long high speed run . Around town starting and stopping all the time fuel consumption is bound to get a little worse .
With my 81 which was formally a 12v with a knackered auto trans that overheated very often and converted it to a 24v (ft) and the manual trans...

Running 35's with the auto gearing is so good!

So there is a massive benefit with the essentially "regear" The best mpg on mine was 25.9 and last fill up got 24.8 when was 12v auto same tyres 16 mpg.

If you haven't run with that setup... then you will never know the benefit of it., or how much better the truck is pulling.. from many miles of experience.